This application is based on application No. 2000-39522 filed in Japan, the content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an optical head, particularly, an optical head for performing recording, reproduction and erasure by use of near-field light, and an optical recording and reproducing apparatus having the optical head.
2. Description of the Prior Art
In recent years, to realize high density recording by using light, a solid immersion technology has been proposed. This technology is to form a minute light spot of not more than 100 nm by reducing the wavelength of light by disposing a high refractive index material between an objective lens and a record medium. As the high refractive index material, although liquid (oil or water) is frequently used in the field of high resolution microscopes, in the field of optical recording, a solid immersion lens or a solid immersion mirror is used to form an optical head.
In such an optical head, a solid immersion lens or a solid immersion mirror is disposed at a distance shorter than the wavelength of light from the surface of the record medium so that the numerical aperture (NA) of light condensation is large, that is, the spot of light condensation is small, thereby realizing high density recording.
In this type of optical head, when some configurations of solid immersion mirrors are used, it is desirable to use only the zonal part of the incident beam without using the central part thereof. Moreover, there are cases where it is desirable to use only light of the high numerical aperture part in order that the spot of light condensation is small on the solid immersion lens or the solid immersion mirror. To obtain such incident light, it is considered to intercept the central part of the beam. However, this reduces the efficiency of use of light, which leads to reduction in the efficiency of recording and the like and reduction in speed.
An object of the present invention is to provide an improved optical head and optical recording and reproducing apparatus.
Another object of the present invention is to provide an optical head and an optical recording and reproducing apparatus in which the efficiency of use of light is increased to solve the problems of reduction in the efficiency of recording and the like and reduction in speed.
The above-mentioned objects are achieved by an optical head comprises a near-field light generating element which generates near-field light; and a beam splitter which splits an incident light into a plurality of beams and directs the split beams to said near-field light generating element.
According to the optical head having the above-described structure, the light emitted from the light source portion is split into a plurality of beams, incident on the zonal part of the near-field light generating element, and condensed inside the element. Consequently, the light emitted from the light source portion is effectively used without being intercepted, and the light can be condensed to a minute spot, that is, the numerical aperture can be increased.
Moreover, an optical head of another structure comprises a near-field light generating element which generates near-field light; and a beam shaper which shapes an incident beam into a substantially toroidal beam and directs the shaped beam to said near-field light generating element.
According to the optical head having the above-described structure, the light emitted from the light source portion is shaped into a substantially toroidal beam without being intercepted, incident on the zonal part of the near-field light generating element, and condensed to a minute spot. That is, only the light of the high numerical aperture part is used with efficiency, and the light can be condensed to a minute spot.